In a standard wellhead, a stuffing box is used to provide a rotary seal around the polish rod of a rod string, which is used to drive a downhole pump. A typical stuffing box is constructed of a generally tubular housing that is threaded onto an upwardly projecting portion of a wellhead. The polish rod extends through the wellhead and through the stuffing box housing. An annular space is formed between stuffing box housing and the polish rod. Typically, a stack of compressible packing rings are positioned in the annular space to form a seal around the polish rod. An internal radial shoulder in the stuffing box housing supports the packing rings at a bottom end of the stack. An annular packing gland is typically positioned at the top of the stack of packing rings. An internally threaded compression nut is threaded onto an externally threaded upper end of the stuffing box housing to force the packing gland downwardly to compress the packing rings against the radial shoulder of the stuffing box housing. When the packing rings are compressed, the packing rings experience radial expansion, so that the rings seal against the polish rod and also against the inside surface of the stuffing box housing.
Problems associated with typical stuffing boxes include leakage and packing wear. A problem with progressive cavity pumps in particular is that the rod string is oftentimes not perfectly straight. Additionally, the rod string tends to oscillate during rotation, which can exacerbate packing wear and may result in the escape of pressurized well fluid.
Therefore, it is desirable to provide a stuffing box having a primary and a secondary seal to increase reliability of the stuffing box. It is further desirable to be able to detect when the primary seal has developed a leak so that repairs can be made before well fluid can escape. Once primary seal leakage is discovered, it is desirable for the stuffing box to have features that enable the stuffing box to be adapted for continued use with the secondary seal until such time as repairs can be made in a convenient and cost effective manner. Additionally, it is desirable to provide a sleeve for shielding the polished rod from sealing elements during operation to avoid polish rod wear.